Two councils met at Constantinople over Photius, in 869 and again in 879, and they reached opposite conclusions. Rome counts the first as the eighth ecumenical council; the East counts the second as a council that annulled it. So the numbering of the ecumenical councils diverges at eight, and a list that runs past seven is telling you which communion wrote it. Both are in this dataset, with their scope marked.
East and West: The Making of a Rift in the Church · ch. 5